Fatigue (medical)

The word fatigue is used in everyday life to describe a range of afflictions, varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles. It can be both physical and mental. Physical fatigue is the inability to continue functioning at the level of one's normal abilities[1][2][3]. It is ubiquitous in everyday life, but usually becomes particularly noticeable during heavy exercise. Mental fatigue, on the other hand, rather manifests in somnolence.

Types

Physical Fatigue

Physical fatigue or muscle weakness (or "lack of strength") is a direct term for the inability to exert force with ones muscles to the degree that would be expected given the individual's general physical fitness. A test of strength is often used during a diagnosis of a muscular disorder before the etiology can be identified. Such etiology depends on the type of muscle weakness, which can be true or perceived as well as central or peripheral. True weakness is substantial, while perceived rather is a sensation of having to put more effort to do the same task. On the other hand, central muscle weakness is an overall exhaustion of the whole body, while peripheral weakness is an exhaustion of individual muscles.

Mental fatigue

In addition to physical, fatigue also includes mental fatigue, not necessarily including any muscle fatigue. Such a mental fatigue, in turn, can manifest itself both as somnolence (decreased wakefulness) or just as a general decrease of attention, not necessarily including sleepiness. In any case, this can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. For instance, a person who is sufficiently somnolent may experience microsleeps. However, objective cognitive testing should be done to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness.

Causes

Fatigue is typically the result of working, mental stress, jet lag or active recreation, depression, and also boredom, disease and lack of sleep. It may also have chemical causes, such as poisoning or mineral or vitamin deficiencies.

The sense of fatigue is believed to originate in the reticular activating system of the lower brain. Musculoskeletal structures may have co-evolved with appropriate brain structures so that the complete unit functions together in a constructive and adaptive fashion.[4] The entire systems of muscles, joints, and proprioceptive and kinesthetic functions plus parts of the brain evolve and function together in a unitary way.[5]

Diseases

Temporary fatigue is likely to be e.g. common cold. Chronic fatigue, on the other hand, meaning of six months or more duration, is a symptom of a large number of different diseases on conditions.

Medications

Fatigue in Aviation Operations

In 1999, the National Aeronautics and Space Administration, NASA, testified before the U.S. House of Representatives that pilot fatigue impacts aviation safety with "unknown magnitude". The report cited evidence of fatigue issues in areas including aviation operations, laboratory studies, high-fidelity simulations, and surveys. The report indicates that studies consistently show that fatigue is an on-going problem in aviation safety [7].

A November 2007 report by the National Transportation Safety Board indicates that air crew fatigue is a much larger, and more widespread, problem than previously reported [8]. The report indicates that since 1993 there have been 10 major airline crashes caused by aircrew fatigue, resulting in 260 fatalities. Additionally, a voluntary anonymous reporting system known as ASAP, Aviation Safety Action Program[9], reveals widespread concern among aviation professionals about the safety implications of fatigue. The NTSB published that FAA's response to fatigue is unacceptable and listed the issue among its "Most Wanted" safety issues [10].

Fatigue in Military Flight Operations

In the late 1990s the US Air Force began testing and developing the Fatigue Avoidance Scheduling Tool, FAST, to address the problem of aircrew fatigue in aircrew flight scheduling [11]. According to the Air Force Research Lab, Human Effectiveness Directorate, FAST is a fatigue forecasting system developed by NTI (and SAIC) under a small business innovative research (SBIR) grant from the US Air Force. Fatigue predictions are derived from the Sleep, Activity, Fatigue, and Task Effectiveness (SAFTE(tm)) model invented by Dr. Steven Hursh, currently the President of the Institutes for Behavior Resources and Adjunct Professor of Behavioral Biology, Johns Hopkins University School of Medicine. The SAFTE(tm) model has received a broad scientific review and the DoD considers it a complete, accurate, and operationally practical model to aid operator scheduling[12].

After several years of attempting to integrate proactive fatigue risk mitigation into Air Force scheduling, the FAST model fell into mainly a mishap analysis role. Since its 2003 release, FAST was primarily used by the Air Force to investigate fatigue factors in aircraft mishaps, after the fact [13]. Following an aircraft mishap, Air Force crash investigators would consult fatigue and human performance experts at the Air Force's Brooks Human Performance Lab in San Antonio, TX. The physiologists and scientists at the lab would run the FAST model to determine the impact, if any, of aircrew fatigue on the mishap. The tool required expert level knowledge of the data input methods and was ideally suited for analyzing historical flying schedules, but did not achieve widespread use in prevention or future scheduling.

In early 2007, the 201 Airlift Squadron of the District of Columbia Air National Guard, successfully integrated FAST into its daily scheduling operations. This integration required the full-time attention of two pilot schedulers, but yielded valuable risk mitigation data that could be used by planners and leaders to predict and adjust critical times of fatigue in the flight schedule. In August 2007, the Air National Guard Aviation Safety Division funded a project to improve the User Interface of FAST, permitting daily use by pilot schedulers and integration with automated flight scheduling software [14].